Display screen or portion thereof with a graphical user interface



The sole FIGURE is a front view of a display screen or portion thereof with a graphical user interface showing our new design.

The outermost broken line rectangle illustrates a display screen or portion thereof. The remaining broken lines illustrate portions of the graphical user interface. None of the broken lines forms part of the claimed design. 

CLAIM We claim the ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 